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Base theme by DesignModo & ported to Powered by Vanilla by Chris Ireland, modified by the "theFB" team.
Comments
Are those transformers tested to 2kV or so primary to secondary and frame? A valve OPT has to stand DC HT plus the peak AC which can be a kV or more if the impedance is mismatched and the stage driven hard.
A 100V line traff only has to cope with 200V peak tops. IF you use one FFS make sure the secondary is well tied to chassis and the chassis earthed! They are also not designed to cope with standing DC but I guess the consequent distortion appeals !
Dave.
Can't speak for the voltage handling capabilities, all I can say is I've tested my amps by running flat out for a good period of time without any undue consequences. But I will email the seller and see if I can get some test specs.
If you're not sure what this is - remove R1(68K, far too low, causes muddy tone) and R7 (1M, reduces gain, unnecessary) and fit the 1M from R7 in the R1 position.
For even more gain remove R6 (1M) and replace it with the 68K from R1.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
http://www.guitar-bass.net/gear/award-session-bluesbaby-22-review/
Would you recommend putting a different value in the R7 position, or is it completely unnecessary?
I think there are also a couple of mods I've seen to reduce noise, like an extra capacitor on the power supply and adding a wire or two to move one of the connections off the PCB.
The R1 change makes a huge difference - the stock 68K resistor is like using the 'low' input on a classic 2-input amp, or having a tone-sucking vintage pedal permanently in line.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
It's a long time ago so I can't remember everything I did. I think I remember doing something to the power supply. I'm pretty sure I've got one of the stock filter caps at home which I replaced with a bigger value. After a valve rectifier you don't use a really big value for the first filter cap. They copied the cap value from the Champ circuit but put a solid state rectifier in it so you can improve power supply filtering by using a bigger value cap. There may have been something to drop the voltage on the power valve as well, as it ran that very hot.
There used to be whole websites dedicate to modding Valve Jrs.
I would say to anyone looking for a 5W amp that I think the VHT Special 6 is a much better sounding amp.
"After a valve rectifier you don't use a really big value for the first filter cap. They copied the cap value from the Champ circuit but put a solid state rectifier in it so you can improve power supply filtering by using a bigger value cap. "
Aha! C'Man. There is thread in 'another place' about a single ended Fender which has Silicon rects but also two 220Rs in series with each leg. I have opined that this is also just a straight copy/hangover from the valve rectifier which needed stoppers for its protection* . Others disagree, saying it is an attempt to introduce 'sag' . Personally, I would have though that by the time you had got a single OP valve to be that far out of 'class A' things would sound terrible?
Mind you, a bigger res' cap is always a good idea for SE amps..They hum!
*Although very few guitar amps that I have seen maps of HAVE anode stoppers for the rect? The data sheets for VRects give tables for transformer impedance and maximum res' caps. The Mullard Valve amp Construction book goes into great detail about this. Its is of course POSSIBLE that the gitamp mains traffs were VERY carefully designed so that they needed no external resistors?
Ooo! Look! A pig just flew past!
Dave.
http://i.imgur.com/iiSNrTb.jpg
Which mods has your modded one got? It looks like an EQ circuit or some description has been added?